HMX, which is known as 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane, is the most powerful non-atomic explosive in military use. However, widespread use of this explosive has been limited by its excessive cost. Although HMX was first discovered in 1941, the only known process for its manufacture is the Bachmann Process but this is limited in its industrial applicability. The latter process has only been demonstrated in batch mode, and requires large excesses of reagents.
In spite of the difficulties of production, and the resulting high price, HMX has gained wide reputation as the most powerful nitramine explosive. In fact, HMX is the undisputed benchmark for all other explosives.
HMX would be applied more widely, however, if two short comings could be overcome, viz. The price of the material, and its impact sensitivity.
The first of these problems has been eliminated. The second problem has been attempted to be solved by various formulations, and compositions, all of which sought to modify its sensitivity through the inclusion of additives, both active and inert.
HMX has four polymorphs viz. Alpha, Beta, Gamma, and Delta. Three of these are stable enough to be prepared, and isolated. Delta is the only one of the four, which is unstable enough in the explosive art to be of no significance. Only trace amounts of this polymorph have been prepared for analytical purposes. Long standing reports clearly indicate that only the Beta polymorph should be considered useful, and safe. It is useful because of its high density, and safe because of its lack of sensitivity to shock. The literature indicates that Alpha and Gamma HMX are comparable to lead azide in terms of its shock sensitivity, and therefore are dangerous.
The most recent attempts to reduce the shock sensitivity of HMX have centered upon the use of small particle size in combination with additives. In the art, Beta HMX having an average particle size of 5 microns is known as Class 5 Beta HMX.